DC/DC converter circuits are used to receive an input DC voltage and output an output DC voltage. Typically, the output DC voltage is different than the input DC voltage. For example, a DC/DC converter circuit may act as a step-down DC/DC converter that outputs an output DC voltage that is less than the input DC voltage. The DC/DC converter circuit may act as a step-up DC/DC converter that outputs an output DC voltage that is greater than the input DC voltage. DC/DC converter circuits may also be used for other purposes, such as to provide noise isolation or regulate voltage levels.
Referring now to FIG. 1, an exemplary DC/DC converter circuit 10 includes a converter circuit 12 and a converter control module 14. The converter circuit 12 receives an input voltage 16. The converter control module 14 generates one or more switching control signals 18. The converter circuit 12 generates output voltage signals 20 according to the input voltage 16 and the switching control signals 18. In a bi-directional DC/DC converter circuit, current flows out of the converter circuit 12 in first and second directions. Current may flow in a first direction in a first operating mode and in a second direction in a second operating mode. In this manner, an AC output of the converter circuit 12 is bi-directional.
It may be desirable to sense an output current through a load or another portion of the DC/DC converter circuit 10 to perform various adjustments of the DC/DC converter circuit 10. The DC/DC converter circuit 10 may be adjusted when the output current exceeds a predetermined threshold and/or when the output current is not equivalent to a desired output current. A current sensing device (not shown) may be used to sense the output current. For example, the current sensing device may sense a voltage drop across a sense resistor 22 to determine the output current.
A DC/DC converter circuit 24 may include a current sensing device 26 that further includes a current transformer 28 as shown in FIG. 2. The DC/DC converter circuit 24 includes a converter circuit 12 that receives an input voltage 16 and generates output voltage signals 20 as previously described with respect to FIG. 1. A converter control module 14 generates one or more switching control signals 18.
The current sensing device 26 communicates with the DC/DC converter circuit 24 to determine an output current (i.e. a current through a load connected to output voltage signals 20) of the DC/DC converter circuit 24. The current sensing device 26 receives a current signal 30 that is indicative of current through one or more components of the DC/DC converter circuit 24. The bi-directional current signal 30 is further indicative of the output current of the DC/DC converter circuit 24.
The current signal 30 flows through the current transformer 28. The current transformer 28 generates a second current signal 32 according to the current signal 30. A rectifier diode 34 receives the second current signal 32 and generates a rectified sensing current signal 36 accordingly. The sensing current signal 36 flows through a resistor 38. In this manner, a value of the sensing current signal 36 can be determined according to a voltage at a voltage sensing node 40.
Typically, current transformers (i.e. current sense transformers) are used to measure current trends, peak values, and average values for purposes of current limiting and/or control. As described in FIG. 2, the current sensing device 26 comprising the current transformer 28 forms a feedback loop that provides current information to the converter control module 14 for use in pulse width modulation (PWM) control. Current transformers provide voltage isolation between the sensed current and the output current and improve the overall efficiency of the DC/DC converter circuit. Current transformers are often preferred over other methods such as described in FIG. 1.
As shown in FIG. 2, the current transformer 28 includes a primary winding 42 and a secondary winding 44. Typically, current transformers use a single turn primary winding to minimize power loss and increase a signal to noise ratio. During operation, the current sensing device 26 senses current as described above when the current signal 30 is flowing in a first direction. A transformer core 46 acquires magnetizing energy as a result of the current flow. When the direction of the current signal 30 reverses according to operation of the converter circuit 12, current flowing through the primary winding 42 reverses. However, the magnetizing energy stored in the transformer core 46, as well as magnetizing inductance characteristics of the secondary winding 44, prevents the secondary winding 44 from providing an accurate indication of the current signal 30.
As a result, typical current sensing devices require the current transformer 28 (i.e. the stored magnetizing energy) to be reset. For example, the current sensing device 26 may include a resetting diode 48 that blocks current flow through the secondary winding 44 when the current signal 30 is flowing in a second direction. In this manner, the current transformer 28 resets during a reset period following transitions of the bi-directional current signal 30 from the first direction to the second direction. As such, the current sensing device 26 is not able to provide current sensing during reset periods.